Developed-market equities have become heavily concentrated in the U.S., creating a wide gap between its market and economic weights. As of April 30, the U.S. made up 72% of the MSCI World Index by market capitalization, while generating 48% of developed-market GDP — a gap of roughly 25 percentage points. That U.S. weight is itself narrowly concentrated, with a handful of large technology companies accounting for a substantial share of it. For investors, this means a portfolio that looks globally diversified by design can still carry substantial country, sector and single-name concentration — something worth checking rather than assuming away through broad geographic diversification.